Rails - Jul 2009 - [ActiveRecord::Base].collect {|a,b| ...} weirdness

Hey everyone.

My mind has been boggled by an issue I ran into a few hours ago. I am
completely lost as to why the following code behaves the way it does
and would appreciate any hints from you guys. It would already be
super-helpful if others could post their output for the following so
that I can figure out whether this is weirdness specific to my setup
or a global phenomenon.

So far, ActiveRecord::Base and its descendants are the only classes
with which I see this behaviour and furthermore it seems to be limited
to Ruby 1.9.1.

Mayday!

Thanks,
Niels (about to dig into array.c)

$ ruby --version; rails --version; ruby <<EOR
require "rubygems"
gem "activerecord"
require "activerecord"

puts "\nActiveRecord::Base disappears:"
[1,String,''foo'',ActiveRecord::Base].collect {|a,b| puts
[a,b].inspect}

puts "\nActiveRecord::Base stays:"
[1,String,''foo'',ActiveRecord::Base].collect {|a| puts
[a].inspect}

puts "\nwtf?"

EOR
ruby 1.9.1p129 (2009-05-12 revision 23412) [x86_64-linux]
Rails 2.3.2

ActiveRecord::Base disappears:
[1, nil]
[String, nil]
["foo", nil]
[nil, nil]

ActiveRecord::Base stays:
[1]
[String]
["foo"]
[ActiveRecord::Base]

wtf?

I can confirm that this does not happen with ruby 1.8.6 on my machine.
I don''t have ruby 1.9 installed, so I can''t be much help
beyond that.
Here are my respective outputs with ruby 1.8.6, just as you''d expect:
>> [1,String,''foo'',ActiveRecord::Base].collect {|a,b|
puts [a,b].inspect}
[1, nil]
[String, nil]
["foo", nil]
[ActiveRecord::Base, nil]
=> [nil, nil, nil, nil]
>> [1,String,''foo'',ActiveRecord::Base].collect {|a| puts
[a].inspect}
[1]
[String]
["foo"]
[ActiveRecord::Base]
=> [nil, nil, nil, nil]


On Jul 14, 11:13 am, Niels Ganser
<ni...-BwZ2I9IdS2OB+jHODAdFcQ@public.gmane.org>
wrote:
> Hey everyone.
>
> My mind has been boggled by an issue I ran into a few hours ago. I am
> completely lost as to why the following code behaves the way it does
> and would appreciate any hints from you guys. It would already be
> super-helpful if others could post their output for the following so
> that I can figure out whether this is weirdness specific to my setup
> or a global phenomenon.
>
> So far, ActiveRecord::Base and its descendants are the only classes
> with which I see this behaviour and furthermore it seems to be limited
> to Ruby 1.9.1.
>
> Mayday!
>
> Thanks,
> Niels (about to dig into array.c)
>
> $ ruby --version; rails --version; ruby <<EOR
> require "rubygems"
> gem "activerecord"
> require "activerecord"
>
> puts "\nActiveRecord::Base disappears:"
> [1,String,''foo'',ActiveRecord::Base].collect {|a,b| puts
[a,b].inspect}
>
> puts "\nActiveRecord::Base stays:"
> [1,String,''foo'',ActiveRecord::Base].collect {|a| puts
[a].inspect}
>
> puts "\nwtf?"
>
> EOR
> ruby 1.9.1p129 (2009-05-12 revision 23412) [x86_64-linux]
> Rails 2.3.2
>
> ActiveRecord::Base disappears:
> [1, nil]
> [String, nil]
> ["foo", nil]
> [nil, nil]
>
> ActiveRecord::Base stays:
> [1]
> [String]
> ["foo"]
> [ActiveRecord::Base]
>
> wtf?

Thanks Steve!

I''ve just set up an isolated virtual machine for testing this out a
bit further. On a vanilla Ubuntu installation with 1.9.1p129 (latest
stable release) this also occurred. Using a current nightly snapshot
(of what will probably become 1.9.2) however, everything works as
expected.

I am still puzzled by this but for the time being happy to just use
Ruby nightlies. If anyone following Ruby development closely could
shed some more light on this that would be great though!

Best,
Niels

On Jul 14, 8:21 pm, JangoSteve
<schwartz.st...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I can confirm that this does not happen with ruby 1.8.6 on my machine.

Niels Ganser wrote:
[...]
> If anyone following Ruby development closely could
> shed some more light on this that would be great though!
Since this doesn''t seem to be a Rails issue, you will probably have 
better luck attracting the attention of the Ruby core team if you post 
to the Ruby list.  Good luck!
> 
> Best,
> Niels
Best,
--
Marnen Laibow-Koser
http://www.marnen.org
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org
-- 
Posted via http://www.ruby-forum.com/.

On Jul 15, 5:57 am, Marnen Laibow-Koser <rails-mailing-l...@andreas-
s.net> wrote:
>
> Since this doesn''t seem to be a Rails issue, you will probably
have
> better luck attracting the attention of the Ruby core team if you post
> to the Ruby list.  Good luck!
You are of course right, Marnen. But for the unlikely case that anyone
else stumbles over this: starting with r24054 (1.9.1-p218) everything
works as expected again.

Apparently it was an issue with ActiveRecord::Base redefining
respond_to? as r24054 is a result of this bug report:
http://redmine.ruby-lang.org/issues/show/1723

For those interested, I reproduced the corresponding change below.

Best,
Niels

--- vm_insnhelper.c     (revision
24053)
+++ vm_insnhelper.c     (revision
24054)
@@ -761,7 +761,7
@@
     int
i;
     int argc orig_argc;
     const int m = iseq-
>argc;
-    VALUE
ary;
+    VALUE ary,
arg0;
     int opt_pc 0;

     th->mark_stack_len argc;
@@ -771,15 +771,19
@@
      *  => {|a|} => a = [1,
2]
      *  => {|a, b|} => a, b = [1,
2]
 
*/
+    arg0 = argv
[0];
     if (!(iseq->arg_simple & 0x02) &&          /* exclude {|a|}
*/
             (m + iseq->arg_post_len) > 0 &&    /* this process is
meaningful
*/
-            argc == 1 && !NIL_P(ary = rb_check_array_type(argv[0])))
{ /* rhs is only an array
*/
+            argc == 1 && !NIL_P(ary = rb_check_array_type(arg0))) { /
* rhs is only an array
*/
         th->mark_stack_len = argc = RARRAY_LEN
(ary);

         CHECK_STACK_OVERFLOW(th->cfp,
argc);

         MEMCPY(argv, RARRAY_PTR(ary), VALUE,
argc);
     }
+    else
{
+        argv[0] arg0;
+    }

     for (i=argc; i<m; i++)
{
         argv[i] Qnil;